1. Field of the Invention
The present invention relates to a method of manufacturing a casting of a Ni-base directionally solidified alloy (hereinafter referred to as "Ni-base DS alloy"), which is used for forming turbine blades and turbine vanes for jet engines and industrial gas turbines.
2. Description of the Related Art
Generally known commercial Ni-base DS alloys include IN792 (9.0 wt. % Co, 12.7 wt. % Cr, 2.0 wt. % Mo, 3.9 wt. % W, 3.2 wt. % Al, 3.9 wt. % Ta, 0.21 wt. % C, 0.02 wt. % B, 4.2 wt. % Ti, 0.10 wt. % Zr, and the balance of Ni), Rene 80 (9.5 wt. % Co, 14.0 wt. % Cr, 4.0 wt. % Mo, 4.0 wt. % W, 3.0 wt. % Al, 0.17 wt. % C, 0.015 wt. % B, 5.0 wt. % Ti, 0.03 wt. % Zr, and the balance of Ni) and Mar-M247 (10.0 wt. % Co, 8.5 wt. % Cr, 0.65 wt. % Mo, 10.0 wt. % W, 5.6 wt. % Al, 3.0 wt. % Ta, 1.4 wt. % Hf, 0.16 wt. % C, 0.015 wt. % B, 1.0 wt. % Ti, 0.04 wt. % Zr, and the balance of Ni). Although inferior in strength at elevated temperature to Ni-base single crystal alloys (Ni-base SC alloys), these Ni-base DS alloys have no directional property when cast and are less subject to cracking. Therefore products of these Ni-base DS alloys are manufactured at a high yield and do not require complicated heat-treatment processes.
Raising the temperature of a combustion gas for driving turbines is the most effective method of improving the efficiency of jet engines and industrial turbines. Therefore it is desired that Ni-base DS alloys having further enhanced strength at elevated temperature, ductility and high-temperature corrosion resistance are developed.